Premium
Structural and Luminescence Study of the 3:2 Complex between Europium Nitrate and the B Isomer of Dicyclohexyl‐18‐crown‐6
Author(s) -
Moret Emmanuel,
Nicolò Francesco,
Plancherel Dominique,
Froidevaux Pascal,
Bünzli JeanClaude G.,
Chapuis Gervais
Publication year - 1991
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19910740109
Subject(s) - chemistry , europium , luminescence , nitrate , crown (dentistry) , stereochemistry , combinatorial chemistry , organic chemistry , ion , dentistry , optoelectronics , medicine , physics
The crystal and molecular structure of bis [ dinitrato ‐( 2,4,8,15,18,21 ‐ hexaoxatricyclo [ 20.4.0.0 9,14 ] hexacosane ) europium ( III )] pentakis ( nitrato ) europiate ( III ) [Eu(NO 3 ) 2 L B ] 2 ([Eu(NO 3 ) 5 ]), has been determined at 170 K from single‐crystal X‐ray diffraction. The complex crystallizes in the monoclinic space group P 2 1 / n ( ITC No. 14): a = 16.338(3) Å, b = 15.704(3) Å, c = 24.474(4) Å, β = 97.73(1)°, Z = 4. The structure was refined to a final R value of 0.058 ( R w = 0.060). The asymmetric unit contains three independent ions lying on general positions: [Eu(NO 3 ) 5 ] 2− and two distinct [Eu(NO 3 ) 2 L B ] + cations with the macrocyclic ligand in the cis ‐ anti ‐ cis conformation ( B ‐isomer). The Eu III ions are 10‐coordinate with the following mean bond lengths: Eu–O(nitrate) = 2.48(2) Å in the anion and 2.45(2) Å in the two cations, Eu–O(ether) = 2.56(8) and 2.55(5) Å. Small but significant differences are observed between the two complex cations, especially with respect to the positions of the cyclohexyl substituent. A conformational analysis performed on the six O‐atoms of the complex cations confirms the predictions of a simple model. The metal ion sites of the complex have been probed by high‐resolution excitation and emission spectra at 296 and 77 K. The 5 D 0 ← 7 F 0 excitation spectrum displays two main bands along with several other minor components. A detailed analysis of the corresponding and selectively excited emission spectra leads to the observation of three types of spectra corresponding to the three crystallographically different Eu III ions. Moreover, three minor sites are identified, one anionic and two cationic, with a population equal to ca. 10% of the population of the main sites. We interpret this finding as reflecting the presence of molecules with slightly different conformations.